Same conductor size in different power cords have different Amp ratings.

[Opcom]

I'm trying to understand how a smaller gauge of power cable handles a higher current.
The two cable types below are both 4-conductor, so as for 120/240V and GND, as in  reguar USA 240V household juice.

Type "SOOW". It needs to have 4-gauge conductors to handle 60 Amps. The typical big black cable.

Type "W". It only has to have 8-gauge conductors to handle 65 Amps. No idea what it looks like. Looking up the same thing in 4-gauge size, that is rated 114 Amps!

How does one handle 60A with 4 Gauge conductors, and the other can handle 65A with the smaller 6 gauge conductors? It does not make any sense.

[KD6VXI]

The conductors are rated for different temperatures.

This is where we, as electricians, have to do yhr math on what we are connecting to.

Not to mention, SOOW cord is temporary only.

At least, code says it is.  Couldn't tell you how many power cords I've made out of SOOW.

I rate SOOW the same way as THHN.  8 gauge is 45 amps.

--Shane
WP2ASS / ex KD6VXI

[W1RKW]

isn't the conductor temperature rating dictated by the insulation type, thickness and spacing and how it can pass or radiate heat?

[KD6VXI]

Yes.

As well as limited by the device it's connected to.

IE, if you have 90c rated wire and 75c rated breakers (or switches, outlets, what have you) then the engineer (electrician) is required to do a thermal calc on the wire to limit current to a value that won't allow the wire to reach a temp over the connections rating.

It's usually easier to just upside the wire.

--Shane
WP2ASS / ex KD6VXI

[Opcom]

Very interesting! Yall gave me a lot to think about and to research. The reason I'd broached the subject is that a detachable power cord about 20FT long has to be made up and I hadn't made up a power cord this large Amp-wise. - so I explored all the different kinds of flexible 4-conductor wire. The more flexible the better.

From what was said, the temperature rise depends on many more factors than the wire size.  Maybe it's nit-picking because an 8 gauge will only drop 1.5V at 60A (90W), and the 4 ga. drops 0.7V (28W). I probably want to stick to the larger wire sizes just to keep temperatures down especially at terminations and contacts.  Inside the equipment, the big wiring is #6 THNN but those are single stranded conductors

=====
learned some stuff on the type S and type W power cords, just to compare the two in the same gauge:

The 4 GA type W is $10/FT., EP rubber insulation, jacket OD=1.245", strands:259.  
-More flexibe because of more strands or the rubber? who knows. Maybe more durable since it's for mining.

4/4 SOOW on the other hand is but $7.12/FT., EPDM insulation, jacket=1.00, strands: 119/25

=====
The 60 amp  connectors for this:
A Hubbell 460B12W is the chassis-mount power inlet, and a 460C12W (these are rating 75 deg C) is the connector on the end of the power cord which will plug into that. I aready have these connectors. The far (wall) end of the power cord will probably be a standard 60A dryer plug and receptacle. -so that is def a limiting factor in the wire size of the cord,

There are industrial Hubbell type of these same connectors but reversed polarity for the 'wall' end of the power cord, but all of these connectors are obscenely expensive. I got some cheap by trading and from ebay.

The inexpensive residential dryer receptacle and plug exist only for the 'wall' end of the cord. There are no reversed-polarity counterparts that I might have used at the chassis (and dryers have no detachable power cords), soo... had to go to an industrial connector set at the equipment if I wanted a detachable power cord.


some links to the wire, but I'm not sure now if that large a size is needed.
https://www.wireandcableyourway.com/4-awg-4c-type-w-portable-power-cable

https://www.wireandcableyourway.com/4-4-soow-portable-cord-600v-non-ul

and this guy's page is interesting.
https://forums.mikeholt.com/threads/what-is-the-ampacity-for-8-awg-wire-50-or-40.37254/

All this is a learning curve.

[KD6VXI]

Is this for the 3cx3000?

If so, do you REALLY need 60A?

60A is 6 gauge.  I wouldn't do 8.

I have done 8 on a 3000 before. 

Remember peak current draw isnt the same.  Plan on peak current draw for your wire size.

--Shane
WP2ASS / ex KD6VXI

[Opcom]

Is this for the 3cx3000?

If so, do you REALLY need 60A?

60A is 6 gauge.  I wouldn't do 8.

I have done 8 on a 3000 before. 

Remember peak current draw isnt the same.  Plan on peak current draw for your wire size.

--Shane
WP2ASS / ex KD6VXI

You are exactly right - it's for that! Things have been really messed up around here it's been months since I touched it. I have to get some stuff gone from the shop in order to have the room to get back to it, and the power supply is 99% done so the power cord makes sense.

I wasn't thinking about peak vs average, but was considering all modes. I don't hardly ever use sideband. Almost always AM. 

I do not REALLY need 60A since we have regulations to follow, but I like to be ready just in case..
The maximum power budget including inefficiencies is sort of like:
15625W plate supply input
582W filaments
265W SOLA transformer inefficiency
100W controls
912W tube blower
100W cabinet blower
============
17584W
/240V = 73.27A. That is worst case.

I have already been using #6 THHN inside the cabinet. Mainly the primary circuit.
240V inlet ->breaker->mercury contactors->variac->plate transformer.

It's always up for discussion. 8-)

[KD6VXI]

You gots to have the peak current capability to make the positive peaks!

Put a current transformer on, say, a Viking or other plate modulated rig, hook it to a scope to get true peaks.

Modulate an am signal.

This is the same reason I always advocated for the 2879 to have 20A PER transistor.

Sure, the Bird doesn't really care, but when in pep mode I can definitely tell when I'm making the current capability of whatever power source sag.

It's like adding more capacitance to improve peak current ability.

--Shane
WP2ASS / ex KD6VXI

[KD6VXI]

To give a little more info, today im troubleshooting a motor.  Trips out after some time running.

Put the Fluke Power Analyzer on it. 

Split phase 240. 

Look at the difference between arms current and peak current.

Now you see why I say design your wiring around peak current.



Turns out, as I was writing this message a fire broke out in what I was testing.  Stupid lizard got caught between 120 leg and ground, high resistance.  Got red enough to start the insulation on fire.  I hear a pop, look to my left and there is smoke coming out of the disconnect.

Contractor wired this one a couple months ago.  Ended up, primary wires too long, touching a screw head behind everything.  Burned lizard caused enough insulation to melt back and was intermittently shorting out.

Funny thing is, that's on the primary side.  Motor was blowing fuses on the secondary side of the fused switch.  Stupid start windings!!!!

Anyway, Patrick, I hope the graphic shows ya why you need to think of peak current.

That said, 'legal limit am' with my 4000, #6 THHN with a 60A breaker fed fine.  1500 watts with 120 percent peaks.

--Shane
Wp2ass / ex KD6VXI

[Opcom]

Did some calculations for wire length using the AWG table. It makes a huge difference. Right now, #8 is from the breaker box 30 FT to the dryer outlet for the 4-1000 transmitter, which is what I'm plugging in the 3cx to for working on it. It's obvious that wire size will not do.